1. Field of the Invention
This invention relates to spark plugs in general and more particularly to spark plugs for use in internal combustion engines.
2. Background of the Invention
A conventional spark plug includes a metallic shell adapted to be fitted into an opening of an engine wherein an air-fuel mixture is present. This area is typically referred to as a cylinder or combustion chamber within the engine. The shell of the spark plug accommodates a ceramic or other insulating structure through which an electrode extends into the combustion chamber. One end of the electrode is connected to an ignition system that supplies an high energy signal to the spark plug, and the other end of the electrode terminates within the combustion chamber. The spark plug provides an electrical arc or spark required to initiate combustion of the air-fuel mixture within the combustion chamber. A ground electrode (typically a projection or protrusion extending inward from the shell of the spark plug) is disposed in spaced apart relation with the electrode and provides a gap across which a high energy arc is established via the ignition system of the engine. The ground electrode or protrusion is mechanically displaced so that a predetermined distance or air gap is established between the center electrode and the ground electrode.
In systems well-known in the art, the spark plug of an internal combustion engine includes a predetermined spark gap or air gap which is mechanically adjusted prior to installation of the spark plug into a corresponding receptacle of the engine. Normally, the spark gap is adjusted to a length between 0.025 inches and 0.060 inches to provide an arc or spark having desired characteristics necessary for initiating proper combustion of the air-fuel mixture. When the engine is cold, it is more difficult to generate a spark between the electrode and the ground projection than is the case when the engine is hot. Further, it is well known that high load conditions require a small spark gap, where as low load conditions require a larger spark gap for proper combustion of the air-fuel mixture to take place.